Periodic extreme rainfall in a warmer climate due to stronger convectively-coupled waves

TL;DR

This study shows that in a warmer climate, tropical regions may experience periodic extreme rainfall driven by convectively-coupled waves at lower temperatures than previously thought, with implications for future climate scenarios.

Contribution

It demonstrates that global-scale models predict earlier onset of periodic extreme rainfall due to convective waves at lower temperatures than prior small-domain studies.

Findings

Periodic oscillations in tropical precipitation occur at 305-310 K.

The oscillation amplitude reaches around 100 mm/day.

Convectively-coupled waves intensify at lower temperatures, triggering extreme rainfall.

Abstract

Tropical regions may experience periodic extreme precipitation and suffer from associated periodic deluges in a warmer climate. Recent studies conducted small-domain (around 100 km x 100 km) atmospheric model simulations and found that precipitation transitions from a steady state to a periodic oscillation state in a hothouse climate when the sea surface temperature reaches 320-325 K. Here we conduct global-scale atmospheric model simulations with different complexity, and we find that tropical precipitation in convective regions already transitions to a O(10 day) periodic oscillation state with a O(100 mm/day) amplitude at 305-310 K. This temperature is substantially lower than previously reported, and within reach in a century under a high carbon emission scenario. We attribute the onset of the periodic extreme precipitation to the intensification of convectively-coupled waves, which occurs at temperatures much lower than the radiative mechanism responsible for the transition around 320-325 K identified before.